Experimental investigation of turbulent premixed H$_2$-jet flames at high exhaust gas recirculation

This study presents an experimental investigation of a turbulent premixed hydrogen jet flame operating under high exhaust gas recirculation (EGR) rates. Experiments were conducted at a Reynolds number of 10000, exploring flames ranging from pure H$_2$-air mixtures to cases with an EGR rate of 0.67. The flames were carefully adjusted to maintain similar laminar burning velocities, enabling consistent comparisons and revealing a systematic increase in the equivalence ratio (Phi) with higher EGR rates. These operating conditions were derived through a detailed 1D analysis of H$_2$-air-EGR laminar flames using comprehensive chemical kinetics, complemented with measurements of the laminar burning velocities of premixed H$_2$-air-EGR flames. The flow field of the model burner setup and nozzle design was characterized under both non-reactive and reactive conditions using particle image velocimetry (PIV). OH* chemiluminescence imaging did not reveal significant changes in the overall structure of the flame, even as the equivalence ratio varied from Phi = 0.4 (pure H$_2$-air flame) to near-stoichiometric conditions (Phi = 0.77). Selected cases were further investigated using OH planar laser-induced fluorescence (OH-LIF), offering detailed visualization of the flame structure and corroborating the observations from OH* chemiluminescence. ... mehrNO$_X$ emissions remained low across all investigated EGR rates, demonstrating robust emission control. These findings enhance the understanding of hydrogen combustion dynamics under high EGR conditions and provide valuable insights for developing low-emission, high-stability combustion strategies.